The prior art has described the combination of metal salts with polymeric substances, including the use of such salts for complexing organic polymers and resins. Zirconium and zinc, for example, have been employed for the cross-linking of polymer latices. Further, the zirconium and zinc have been used in a complex metal chelate with amine compounds, such as ethylenediaminetetracetic acid for curing acid functional polymers and resins. Such a use is known, for example, in the floor polishing art. When used in that manner, the applied, dried film can be removed only through use of ammonia solutions and other alkalies will not act upon the film. In these uses, the metal ions are attracted to the oxygen-containing groups of the resin and it is for this reason that the ammoniacal solutions will break down the formed film, while other alkalies and detergents will have, essentially, no effect.
For example, the prior art includes disclosures such as in U.S. Pat. No. 3,129,176--Ihde, Jr.--where a metal salt is complexed with a siliceous amino compound which can be used as an additive for printing inks to provide the proper balance of tack, penetration, and viscosity. The amino compound used in that case is a partial amide prepared by reacting a monocarboxylic acid and a polyamine.
Rogers, U.S. Pat. No. 3,320,196, describes a coating composition formed from a polyligand alkali-soluble resin, a polyligand polymer, and a zirconyl-fugitive ligand complex which is capable of undergoing ligand exchange with at least some of the carboxyl groups of the organic film former. One typical complexing agent is ammonium zirconyl carbonate.
U.S. Pat. No. 3,328,325--Zdanowski--teaches a floor polishing composition containing an alkali-soluble resin and the ammonia or amine complex of a polyvalent metal salt where the salt has an appreciable solubility in water. These components form only a minor part of the floor polishing composition which also contains a water-insoluble polymer and a wax. Similar compositions are shown in Fiarman et al, U.S. Pat. No. 3,467,610, and Gehman et al, U.S. Pat. No. 3,554,790.
Ink binder resins have also been neutralized with amine compounds with the formation of ammonium salts. This is shown in a variety of patents including U.S. Pat. Nos. 1,789,783--Silberstrom; 2,449,230--Irion; 2,690,973--Voet; 3,412,053--Pugliese; and 3,470,054--Tyrrell.
In addition to the above, improvements in the usefulness of films formed from acidic resins have been achieved through use of metal compounds, particularly ammonium zirconyl carbonate, and materials similar to it. The use of such zirconium compounds to cross-link polymers formed from aqueous solutions of polyacrylic and polymethacrylic acids is disclosed in U.S. Pat. Nos. 2,758,102--Grummitt et al--and 3,079,358--Uelzmann.
Still further, ostensible complexes of metals, including zinc, with polyalkylene polyamines have been used with resins as catalysts. For example, in British Pat. No. 868,465--Schweizerische Isoia-Werke, published May 17, 1961, a complex formed from an oxide or inorganic salt of a divalent metal, a carboxylic acid or a phenol, and a primary monoamine or polyamine, is employed as the catalyst in the formation of a polyester resin. As pointed out in that patent, however, by the time the polyester resin is formed, the complex has decomposed. Still further, this polymerization is carried out, essentially, under anhydrous conditions. In particular, as noted in Example II, during formation of the complex, the water formed is driven off.
As can be seen, zirconium and zinc are the metals generally employed in the prior art, as they are the most effective known, for cross-linking of acidic resins and other treatments to render them useful in the coating art. While numerous variations exist as to the method of introduction, and the form, of the metal, the performance of all these products is directly dependent on stoichiometry of the metal to the resins' acidity. Primary cross-linking is the result of salt formation between the metal and the resins' carboxyl groups, though some secondary coordination with other hydrophilic groups may occur.
Many other methods exist involving the use of chemical or heat-treatment after film formation to effect improved water resistance, or other useful properties. The prior art also discloses the use of various amines and acidic resins, in both aqueous and organic solvents, to effect improvements in solubility, rheology, and/or final film properties. This is shown, for example, in U.S. Pat. No. 3,615,752--Hoffman, Jr. et al. The use of most amines with acidic resins is limited, however, since these amines tend to form ammonium salts which increase the water-solubility of the resulting films and coatings, due to the amines' limited volatility and residual salt stability. The use of boronated fatty acid polyamide resins in coatings has also been disclosed, as in U.S. Pat. No. 3,786,007--Whyzmuzis et al. Neither of the patents referred to here, however, employed metals for treatment of these acidic resins, except, possibly, alkali or alkaline earth metals.
Despite the extensive prior art, which is represented above, on methods for improving coating compositions derived from solutions of aqueous acidic resins, this resin class remains severely limited in application. In most commercial applications, these resins are used only as modifiers to impart certain desirable properties, such as pigment wetting, but not otherwise, as they lack adequate film performance in critical coating areas when compared to coatings deposited from organic solvents. It is a known disadvantage of water-thinnable resins of this type that, in general, they produce unstable aqueous dispersions and films with lower gloss, poor hardness and abrasion, and poor water-resistance when compared with the conventional, solvent-based coatings.
A further important limitation of known aqueous resin solutions is the higher viscosity of these solutions at the same solids content when compared to solutions of the unneutralized resins in organic solvents. This limitation requires the utilization of a material with a molecular weight insufficient to produce adequate film properties if a workable viscosity is to be maintained. In printing inks, the use of aqueous soluble resins is limited by their inability to dry rapidly and the tendency of water to cause distortion of the paper upon which is is being printed. It is well known in the prior art that printing with water-based inks results in much slower dry rates as compared to similar resin solutions made with volatile, organic solvents. Another known disadvantage of the water-thinnable resins is their inability to wet various non-porous substrates, which results in excessive crawl and poor ink lay.
In protective and decorative coatings, water-thinnable alkyd resins have the known disadvantage that, in general, they produce unstable aqueous dispersions and are characterized by films of poor gloss, hardness, and water-resistance. Numerous methods have been disclosed for improving the performance of such water-thinnable alkyd resins in the preparation of lacquers and paints and, exemplary of such methods, are those disclosed in U.S. Pat. No. 3,376,241--Que. Frequently, these resins are modified by reacting them, either during or after preparation, with drying or non-drying oils, oily fatty acids, resin acids, phenols, urea, or melamine-formaldehyde resins in an effort to improve film-forming properties of these coatings, such as hardness, toughness, and flexibility. Important criteria for commercial acceptance of water-dispersible coating compositions, particularly water-thinnable alkyd resins, are dispersion stability, dilutability with water, ease of preparation, surface adhesion, film-resistance to water and alkali, and the ability to air-dry, particularly in regard to the drying rate and the ultimate properties of the cured material.
The material of the present invention provides for water solutions of acidic resins which eliminate many of the disadvantages referred to above and for a method for preparing such materials.